An MRAM (Magnetoresistive Random Access Memory) is a form of non-volatile computer memory capable of storing bits of digital information (binary 0's or 1's). MRAM digital data is not stored as an electrical charge as in traditional RAM components, rather the bit state (being 0 or 1) is stored via resistive states (high resistance or low resistance) in magnetic storage elements which do not require constant electrical power to retain their state. An example of a magnetic storage device may consist of a pinned (fixed) magnetic layer, a free (variable) magnetic layer, and a non-magnetic conductive barrier layer interposed between the pinned and free magnetic layers. The relative alignment of the magnetic fields of the pinned and free layers determines the resistive state (high resistance or low resistance) of the barrier layer interposed between the pinned and free magnetic layers.
Changing the resistive state of the MRAM device is controlled by changing the magnetic state of the free layer to either match that of the pinned magnetic layer, or oppose that of the pinned magnetic layer. Matching the magnetic orientation of the free layer to the magnetic orientation of the pinned layer creates a low resistive state in the barrier layer, whereas the stored memory bit information equals the binary value of, for example, 1. Having opposed magnetic orientation between the magnetic free layer and the magnetic pinned layer (the magnetic orientation of the free layer opposes the magnetic orientation of the pinned layer) creates a highly resistive state in the barrier layer, whereas the stored memory bit information equals the binary value of, for example, 0. Typically an MRAM device is formed by placing the pinned, barrier, and free layers between two electrodes in a semiconductor device.
An MRAM device may have operations to set and retrieve data such as read, write-1 (set to value=1) and write-0 (clear set to value=0). Write operations, also called programming operations, apply electrical pulses to the electrodes thereby causing current to flow between the pinned and free layers of the device. Depending upon the direction of the current flow, the magnetic orientation of the free layer will change to either match or oppose the magnetic orientation of the pinned layer. Read operations are also performed across the electrodes by measuring the resistance between the pinned and free layers of the MRAM device.